The present invention relates to a method and apparatus for suppressing stochastic interference signals in ultrasonic distance measurements. The apparatus comprises an ultrasonic proximity initiator that repeatedly sends out ultrasonic pulses of equal width and receives corresponding echo signals that are evaluated in a control and evaluating unit. Stochastic interference appears as deviations in the echo signals as measured relative to the emitted ultrasonic pulses. These deviations are compensated for in the distance determination.
Methods for suppressing the foregoing type of interference are known, for instance, from U.S. Pat. No. 4,649,527, corresponding to DE 3,428,773. This reference distinguishes false pulses based on pulse width since false pulses can be recognized as being wider or narrower than the emitted ultrasonic pulses, all of which have an equal width. While effective at limiting false releases, this method has the disadvantage that the evaluation is only very coarse as to whether or not an echo signal carries interference since the information contained in the amplitude of the echo signal is not considered.